Having done a bit of cleaning up of the 1973 fillet-brazed Sports Tourer now, I have discovered a few surprising things about this model. which may be of interest to those whose interests are not limited to a half dozen Italian marques.
While Nervar cranks seem to have been typical on this model, this particular bike has a rather unusual TA Cyclotourist double. The rings are 54-40, which may indicate this crank is original, since the smallest available ring for the Nervar double more typically supplied on this model was 40T. Perhaps they changed suppliers but kept the same spec for ring size. The crank has something I've not seen before, a double chainguard, one for the outer ring and a second for the inner ring. The two guards are secured to the large ring with six bolts similar to double chainring bolts, using an extra set of holes drilled in the drilled in the 54T ring at a large BCD. I think this is another indication the crank is original, as I've never seen such a crank before and imagine it would not likely have been an aftermarket item.
The gearing seems very high for a touring bike supplied with a Schwinn-badged Crane GS RD. Not only is the the 54T ring awfully large for a double on a touring bike, but the Atom FW is only 14-24, not that low for a tourer. I've already changed out the gears to 50-36 with a 14-32 Simplex FW. Unfortunately, the 50T ring is not drilled for the unusual double chainguard.
Also learned a another new fact about the TA Cyclotourist. The chainring bolts are the old style with domed boltheads to the outside and slotted sleeves/nuts inside the crank, as opposed to the newer style with allen head sleeves outside and hex head bolts inside. I always thought the two types of fasteners could be interchanged, but that is not the case. After changing the rings, I found the chainring bolts would not tighten up completely. The problem is that the old bolts and sleeves are made for an outer ring which does have the countersunk bolt hole found on newer outer rings. When used with newer recessed outer rings, the old domed bolts will bottom out on the sleeve before the rings are completely secured. This could possibly be corrected by shimming the sleeves with washers with a small OD-ID difference, or filing the sleeve, but I just resorted to using newer style hardware. Just another example of the endless variations encountered with TA gear.
Big Spring, Texas, USA